Terminal for electrical cables.



G. W, DAVIS.

TERMINAL FOR ELECTRICAL GABLES.

APPLICATION IILEDHAB. 6, 1909.

941,860. Patented NOV. 30, 1909.

2-SHEETSSHEET 1.

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a J g \1 8 7 7 H; -10 L1 i WITNESSES: 5 Tum/Enron G. W DAVIS.

TERMINAL FOR ELECTRICAL GABLES.

APPLICATION FILED MAR. 6, 1909.

941 860. Patented Nov. 30, 1909.

2 SHEETS-SHEET 2.

F! G- 3 F! E 4- 3 4 Y 3 W l 1 if JfA/QESSES: I 013 INVENTOR CHARLES W.DAVIS, EDGEWQRTH, PENNSYLVANIA.

TERMINAL FOR ELECTRICAL CABLES.

Specification of Letters Patent.

Patented Nov. 30, 1909.

Application filed March 6, 1909. Serial No. 481,633.

To all whom it may concern:

lie it known that I, CHARLES W. DAVIS, residing at Edgeworth, in the.county-of 'Allcgheny and State of Pennsylvania, a

citizen of the United States, have invented or discovered a certain newand useful Improvement in Terminals for Electrical Cables, of whichimprovement the following is a specification.

My invention relates to improvements in terminal structures forelectrical cables; and the objects of my invention are efiiciency toprevent leakage of current and deterioration of material, and simplicityof structure, to cheapen manufacture and to eliminate difiiculty ininstallation.

The invention is primarily concerned with a terminal for a multipleconductor cable, that is, a cable containing two or more separate andindependent current-bearing conductors, each insulated from the other;seeondarily, it is concerned with the particular formation of aninsulator.

Though my improved insulator is peculiarl y applicable to a terminal fora multipleconductor cable, it'will be understood that it is not thuslimited in application, but may be used in terminals of other kinds aswell.

In the accompanying drawings forming part of this s ecification, Figure1 is a top plan view an Fig. 2 a view in vertical section of a terminalembodying my present invention; Figs. 3 and 4 are vlews on larger scaleshowing the insulators in detail and illustrating certain modificationsin the structures thereof.

The purpose of a terminal is to surround and protect the endof afcable,and to afford structural continuity but electrical discontinuit ybetween the sheath of the cable at a point adjacent to its end and theprotruding conductor; it consists essentially of a thimble and aninsulator. The thimble is ordinarily formed of metal, it surrounds andis united upon the surface of the cable sheath. The insulator is anannular body engaging at one end the thimble and at the other end,either immediately or through some interposed structure, engaging theoutward leading conductor. y

In designing a terminal for a multiplecore cable, from which theindividual conductors are to have separate leads-out, the thimble mustof necessity be expanded or enlarged into a casing to engage not asingle insulator only, but several insulators, corresponding in numberto the number of leadsout. It is of course desirable that the structurebe as small as compact and as light as may be, and this requisiteintroduces a problem into the designing of terminals formultiple-conductor cables for the several conductors left protrudingfrom the end of the cable when the sheath is cut away are not readilypliable, they can be made to diverge at relatively small angles only,and accordingly it is not possible to bring all the several insulatorswhich are to surround the leads-out within some considerable distance ofthe end of the" cable sheath.

Referring to Figs. 1 and 2 of the drawings, the terminal there shown isapplied to a three-conductor cable; the cable is indicated at 1 and theseveral conductors at 2. 3 is the thimble, and 4 are the insulatorswhich correspond in number with the conductors of the cable. The thimblesurrounds the end of the cable to the sheath of which it is secured,preferably by a wiped solder joint, as indicated at 5. From the pointwhere it is secured to the cable sheath the thimble 3 flares outwardlyto form a chamber or casing in the wall of which are formed threeorifices for the introduction of three insulators through which thethree conducthe introduction of a thimble to which the sheathed cablemay be secured, and with the holes for the leads-out opposite. Thisstructure is designed to be assembled in the field; the casing isprovided with a hand-hole through which necessary access is had to theinterior for purposes of assembling, that hand-hole being closed by aplate bolted in place. My present improvement in this regard consists ina casing in which all the orifices for the leads-out arran ed oppositethe orifice for the introduced ca le are symmetrically disposed aboutthe prolonged axis of the orifice for the cable, and are further soparticularly placed that the axis of all the several lead-out orificesconverge toward the orifice for the cable. In consequence of suchsymmetrical arrangement of the leadsout, instead of the arrangement ofthem all minimum. I make the casing of light spun metal, dispensing withthe necessity of making the casing and the thimble two separate parts ormembers; and, further, while it is a practical necessity under existingconditions in the art of metal working to complete the enlarged thimblewith a cap or cover 6, the thimble with its cap may be and preferably isassembled in the shop to form in effect a one-piece thimble. Myinsulators are so designed that the structure may beassembled withoutseparating the parts of which this enlarged thimble is composed. This isa distinct practical improvement over prior structures used for thispurpose.

The insulators are secured in the orifices designed to receive them inany desired manner, preferably by the screw thread connection shown.

In order to properly apply the terminal to the cable, not only must thecable sheath be cut away; the insulating envelop of hygroscopic materialalso which lies between the core and the sheath of the cable must beremoved, laying the conductor bare. The bared conductor may then beelectrically united within the terminal to an aerial or other conductorintroduced through the insulator to the interior of the terminal, or itmay be wrapped with non-hygroscopic insulation and carried out throughthe insulator. v

Fig. 8 shows the cable core protruding as a lead-out. In this case thehygroscopic insulation employed in the lead-sheathed cablchas beenremoved, and moisture-proof insulation has been applied. This is done inthe field.

Fig. at shows a covered aerial introduced through the insulator intothe,terminal and there united electrically with the conductor from thecable. It will however be observed that in each case it is requisite tocut away the sheath and insulating envelop of the cable; and, theneither to connect the conductor within the thimble to a water-proofedinsulated lead out, or to normally apply new insulation to the portionof the bared conductor which passes through and beyond the insulator.But whether a joint be made Within the thimble or the conductor be striped and covered again with weatherproof insulation, the insulation isweakened and there will exist within the terminal tendency toelectrostatic discharge and to leakage, from one conductor to itsneighbor, even though the intervening space be filled with someinsulating substance. It therefore becomes desirable to prolong inwardlythe insulator itself, in the form of a sleeve, surrounding such joint.In one case the joint is a joint of the conductor itself; and of itsinsulating envelops, and in the other case the oint is of insulatingenvelops alone. It is ordinarily desirable to have the bore through theinsulator as small as may be and its walls correspondingly thick at thepoint where it passes through the orifice in the casing; it is alsodesirable to have the bore of the insulator enlarged where it surroundsthe joint above alluded to. In the drawings, the inward prolongation ofthe insulator is indicated at 7 and its enlarged bore, 8; Thus the jointis protected, and the structure is not weakened.

My invention is further concerned with the character of the insulatoritself. The insulator is shaped externally to meet the particularconditions of the service for which it is designed, and as illustratedin the drawings this outer surface is corrugated transversely, awell-known device for guarding against leakage, and suited particularlyfor in-door installations, that is, installations where the terminal isnot directly exposed to falling rain and snow. I have found that byforming those surfaces of the insulator where water-tight joints aredesired with a rough or granular finish and applying to such surfacesinsulation preferably in the then,'the insulator being brought to placeupon the wrapped conductor, the water-tight adhesion described iseffected. Again, in case the lead-out is in the form of a weather proofaerial, such as is illustrated in Fig. 4c, the serrated joint 10 withinthe insulator is wrapped with rubber tape 11 to fill the bore of theinsulator at that point and seal the surfaces against the ingress ofmoisture.

In order to effect a more secure sealing of the joint, I preferably layback or bevel the shoulder 12 forined where the bore of the insulator isenlarged inwardly; this surface, inclined to the axis of the bore,constitutes a surface upon which the rubber tape wrapping will becompressed when the conductor is drawn to place within the insulator, toform there a tight joint. The same sort of sealing may be employed tosecure the protruding lead-out and the outer end of the insulator to oneanother in a moisture-proof joint. To this end the insulator is providedwith an extension 13 upon its outer end, and the external surface ofthis extension is made rough or granular. A wrapping 14 of rubber tapeat this point, joining lead out and insulator, will adhere to theinsulator in moisture-proof engagement. In this construction, it will beobserved, such a packing gland as is indicated at 15 in Figs. 1 and 2 isnot necessary.

Ordinarily, the insulator will be formed of porcelain; its exposedsurface will be glazed; but its bore and the surface of the extension 13(if present) will be left with its natural rough, unglazed surface,which is well suited toleffect the described ends. The inward prolonation 7 of the insulator will preferably be deft unglazed externally aswell as internally, for the insulating compound employed to fill thethimble chamber will adhere more firmly to the unglazed surface, toprevent leakage.

The parts are assembled as follows: The

thimble 3, though ordinarily formed in two.

pieces because it may thus be more easily made, may be completed in theshop, and applied in the field as an entirety. The sheath and thehygroscopic insulating envelop of the cable are cut away and the freeends of the conductors are thrust into the inlet orifice in the casing,from which the insulators 4 have previously been removed, spread within,and drawn out through the several exit orifices. The leads-out are thenconnected, and wrapped as may be desired. If the conductors of the cableare themselves led out, the hygroscopic insulating envelop is removedfrom ,the conductor so far as necessary, and the wrappings of tape areapplied upon the severed end of that envelop and the adjacent surface ofthe conductor. The insulator is then applied and secured in place in thecasing. Then each lead-out in turn is drawn outward, and made fast tothe outer end of the insulator, either by means of the packing gland, 15of Figs. 1 and 2,

or the wrappingsl l of tape of Flgs. 3 and4. It will be observed thatthis drawing outward and securing of each lead-out will bring theinternal wrappings of tape to position upon the rough surfaces of theinsulator (where such arrangement is employed) to effect the water-tightadhesion of surfaces already described. The parts being thus brought toproper relative positions, the

it wiped-solder joint 5 between thimble 3 and cable sheath 1 is made,securing the arts. Finally, an insulating substance 1n iquid form may beintroduced to fill the spaces within the thimble through an opening towhich a cap 16 is fitted.

I claim as my invention:

1. In a terminal structure for a multiplecore electrical cable, a casingprovided with an orifice adapted to receive and to be united upon thesurface of a cable introduced therein, and provided also with aplurality of oppositely disposed orifices arranged with their individualaxes converging to said first named orifice, together with annularinsulators filling the last named ori fices and provided withprolongations extending inwardly through said casing toward the orificetherein first named, substantially as described.

2. In a terminal structure for an electrical cable,the combination of acasing and an insulator, said i nsulator consisting of a perforatecylindrical body provided externally with means for attachment in anorifice in the wall of said casing and of a perforate terminalextension, the perforation of the extension being of greater diameterthan the perforation of the body portion of said insulator,substantially as described.

3. A terminal structure for an electrical cable, including a casing andan insulator carried in the wall of such casing, said insulator beingperforated by a bore larger at one end than the other, a portion of thesurface of the bore being arranged obliquely to the axis thereof,substantially as de scribed.

4. A terminal structure for an electrical cable including a casing and aperforate insulator carried in an orifice in the wall of said casing,the surface of the bore of said perforate insulator being rough,substantially as described.

5. A terminal structure foran electrical cable including a casing andaperforate insulator carried in an orifice in the wall of said casing,said insulator being prolon ed inwardly and the outer surface of saiinward prolongation being rough, substantially as described.

6. An insulator for an electrical conductor consisting of a perforatebody provided externally with means of attachment to a support, andhaving a rough exterior surface at one end thereof, substantially asdescribed.

In testimony whereof, I have hereunto set my hand.

CHARLES W. DAVIS.

Witnesses:

CHARLES BAnNErr, EDWARD F. Moses.

